LOOK vulnerable, I guess...but it just bothers me that so many people define the breed by that when not all dachsies have problems. When I tell people I have a mini dachshund, often their very first response is "Oh...those seem like nice dogs. Too bad they all have back problems." THAT drives me nuts, since LOTS of breeds have various health problems but very few are stigmatized in the same way.
It's not just a "long dog" thing, either, as bassets don't have the same problems. So it may be PARTIALLY structural, but not entirely.